This application claims the priority of German patent document 197 02 312.6, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a system for controlling the longitudinal speed of a motor vehicle which contains an operating element that can be actuated to designate a desired longitudinal acceleration value.
In automobiles, the desired longitudinal vehicle speed is conventionally controlled by means of gas and brake pedals. Alternatively, it has been suggested that a control-stick be used as an operating element, at least to initiate positive accelerations, and optionally also to trigger negative accelerations, (that is, deceleration). Thus, for example, in one possible function assignment, actuation of the operating element toward the front can trigger a speed increase and actuation toward the rear can trigger a speed reduction. Arrangements of this type are described in U.S. Pat. No. 3,022,850, and in the publication by H. Bubb "Arbeitsplatz Fahrer--Eine ergonomische Studie" ("Workplace--Driver, An Ergonomic Study", Automobil-Industrie 3/85, Pages 265.
A system in which the operating element can be operated manually, and is preferably constructed as a control stick, is described in German patent document DE 196 00 140.4. In this system, a longitudinal speed control is performed by actuating the operating element in the forward direction for positive acceleration, and toward the rear for negative acceleration.
In accordance with a defined linear characteristic curve, actuation of the operating element determines a desired longitudinal acceleration value as a function of the operating element deflection. To maintain a defined speed despite variations in existing road resistance, the acceleration regulator can be activated with the desired longitudinal acceleration value of zero.
German patent document DE 27 01 567 C2 discloses a speed control device for vehicles in which an adjusting member is provided for designating an acceleration or deceleration defined as a function of the driver's desire. The corresponding acceleration or deceleration desire is processed in a desired speed value generator into a corresponding desired speed value, which will then be supplied to a speed control. By means of a function generator within the speed control, the signal of the adjusting member is processed such that four ranges are formed. Specifically, these are an idling range, a deceleration range, a pressure point range and an acceleration range. If the adjusting member is in the pressure point range, which is situated between 30% and 40% of the overall path of the adjusting member, the vehicle speed is controlled to a constant desired value. When the adjusting member position exceeds or falls below the pressure point range, a corresponding acceleration or deceleration signal is generated.
German Patent Document DE 35 10 174 C2 describes a device for influencing the driving speed of a motor vehicle which comprises an operating part, a speed control, an acceleration control and a condition control which transmits an adjusting signal of the speed control or the acceleration control to a fuel quantity metering device, as a function of the actuating condition selected by the driver via the operating part. Acceleration control is implemented before and/or after the speed control.
The speed control has an integral part which, during the transition from acceleration control to speed control, is set by the condition control to an initial value that corresponds to a quantity-characterizing signal of the fuel quantity metering device before the selection of acceleration control. Specifically, at the end of an acceleration phase, the desired speed value for the subsequent speed control is set to the actual speed value at this time, until the overshooting actual speed has assumed a constant value to which the desired speed will then be newly set.
The object of the present invention is to provide a system of the initially mentioned type which permits a comfortable and ergonomic control and/or regulating of the longitudinal speed of a motor vehicle.
This and other objects and advantages are achieved by the control system according to the invention, in which whenever the desired longitudinal acceleration value designated by the operating element is above a set threshold value (which preferably is very low in comparison to the maximum possible vehicle acceleration), the system adjusts the longitudinal vehicle acceleration to the designated desired acceleration value. When, however, the desired longitudinal acceleration value designated by the operating element falls below the set threshold value, the system controls the vehicle to a constant desired speed value until a new acceleration operation or a deceleration operation is triggered. Such constant speed control is known from conventional speed control devices in the form of so-called cruise controls, which set the vehicle speed to a value equal to the actual vehicle speed existing at the time when the speed control is activated. In contrast, during this speed control phase the present system uses a desired speed value which is smaller than the actual longitudinal speed value at the time of the activation of the respective speed control phase, by a differential value which is defined as a function of the speed.
This technique has the effect that the level of attention and fast reaction demanded of the driver to adjust the desired speed is not as great as it is in the case of systems which control the speed precisely to value existing when the respective control phase is activated. In practice, this means that, after actuation of the operating element, the vehicle first becomes slower by the defined differential value (which is a function of the existing vehicle speed) before its speed is held constant by the speed control part of the system. Driving tests have demonstrated that, in comparison to other conventional systems, this type of longitudinal speed control results in significantly lower stress to the driver.
In one embodiment of the invention, the sensitivity of the relationship between the desired longitudinal acceleration value on the one hand, and the degree of actuation of the operating element on the other, varies as a function of the vehicle speed (specifically decreasing with rising longitudinal speed). In this manner, the slope of the characteristic curve which defines the functional relationship between the degree of actuation of the operating element and the corresponding indicated desired longitudinal acceleration value advantageously takes into account the fact that the acceleration capacity of motor vehicles decreases with rising speed, because the power required to overcome the road resistance increases considerably with a rising speed. In addition, this selection of a speed-dependent sensitivity for the indication of the desired longitudinal acceleration value takes into account the fact that the absolute acceleration value at high speeds is subjectively felt to be higher than at low speeds, because of kinesthetic, acoustic, visual and mechanical information which the vehicle occupants experience. The speed-dependent selection of the sensitivity of the desired longitudinal acceleration value indication is therefore advantageous, for reasons of automotive engineering as well as for ergonomic reasons.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.